Cathodic electrocoating compositions containing an anti-crater agent

ABSTRACT

An improved aqueous cathodic electrocoating composition that contains an anti-crater agent which is a water-reducible polyester resin having an acid value less than 40 mg KOH/g. The water-reducible polyester is the reaction product of (1) a hydroxy cyclic carbonate; (2) a polycarboxylic acid anhydride; (3) optional monofunctional epoxy resin; (4) a polyfunctional epoxy resin; and, (5) a polyamine compound containing tertiary amine and either primary or secondary functionality. The reaction product is neutralized in the presence of acid and water to convert the tertiary amine groups to water-dilutable groups. Hydrolyzable silane groups can also be incorporated into the reaction product to further enhance its crater resistance property. The electrocoat composition produces coatings having a smoother appearance with fewer craters without adversely affecting intercoat adhesion of the cured film to subsequent coating layers applied thereover.

This invention is directed to a cathodic electrocoating composition andin particular to a cathodic electrocoating composition containing ananti-crater agent, which significantly reduces, craters and improves thesmoothness of an electrodeposited film of the composition.

BACKGROUND OF THE INVENTION

The coating of electrically conductive substrates by anelectrodeposition process also called an electrocoating process is awell-known and important industrial process. Electrodeposition ofprimers to automotive substrates is widely used in the automotiveindustry. In this process, a conductive article, such as an autobody oran auto part, is immersed in a bath of a coating composition of anaqueous emulsion of film forming polymer and acts as an electrode in theelectrodeposition process. An electric current is passed between thearticle and a counter-electrode in electrical contact with the aqueousemulsion, until a desired coating is deposited on the article. In acathodic electrocoating process, the article to be coated is the cathodeand the counter-electrode is the anode.

Resin compositions used in the bath of a typical cathodicelectrodeposition process also are well known in the art. These resinstypically are made from polyepoxide resins which have been chainextended and then an adduct is formed to include amine groups in theresin. Amine groups typically are introduced through reaction of theresin with an amine compound. These resins are blended with acrosslinking agent and then neutralized with an acid to form a wateremulsion, which is usually referred to as a principal emulsion.

The principal emulsion is combined with a pigment paste, coalescentsolvents, water, and other additives to form the electrocoating bath.The electrocoating bath is placed in an insulated tank containing theanode. The article to be coated is the cathode and is passed through thetank containing the electrodeposition bath. The thickness of the coatingthat is deposited on the article being electrocoated is a function ofthe bath characteristics, the electrical operating characteristics, theimmersion time, and the like.

The resulting coated article is removed from the bath after a set periodof time and is rinsed with deionized water. The coating on the articleis cured typically in an oven at sufficient temperature to produce acrosslinked finish on the article.

Cathodic electrocoating compositions, resin compositions, coating bathsand cathodic electrodeposition processes are disclosed in Jarabek et alU.S. Pat. No. 3,922,253 issued Nov. 25, 1975; Wismer et al U.S. Pat. No.4,419,467 issued Dec. 6, 1983; Belanger U.S. Pat. No. 4,137,140 issuedJan. 30, 1979 and Wismer et al U.S. Pat. No. 4,468,307 issued Aug. 25,1984.

A continuing problem with cathodic electrocoating compositions has beenthe presence of craters in the cured finish. A number of anti-crateragents have been used in the past to eliminate craters. However, thepresence of conventional anti-crater agents in electrocoatingcompositions has had a negative impact on the adhesion of subsequentcoating layers applied thereto, such as automotive PVC sealers used forsealing joints and primer surfacers, particularly where theelectrocoating film has been cured in an oven without the presence NOx(nitrogen oxides), such as in an indirect gas or electric oven. Anadditive or agent is needed for electrocoating compositions so thatcrater-free, smooth and even finishes are formed on electrodepositionand curing, without adversely affecting the adhesion of PVC sealers andprimers subsequently applied thereto.

SUMMARY OF THE INVENTION

The present invention is directed to an improved aqueous cathodicelectrocoating composition having a binder of an epoxy-amine adduct anda blocked polyisocyanate crosslinking agent; wherein the improvement isthe use of an anti-crater agent comprising a highly branchedwater-reducible polyester having an acid value less than 40 mg KOH/gwhich is the reaction product of:

-   -   1) a hydroxy cyclic carbonate;    -   2) an aliphatic polycarboxylic acid anhydride;    -   3) optional monofunctional epoxy resin;    -   4) a polyfunctional (di- or higher) epoxy resin; and,    -   5) a polyamine compound selected from one of the following two        groups:        -   (i) a polyamine containing a tertiary amine and a primary or            secondary amine group, or        -   (ii) a combination of a polyamine containing a tertiary            amine and a primary or secondary amine group, and an            aminoalkylalkoxysilane,

which reaction product is neutralized in the presence of acid and waterto convert the tertiary amine groups to water-dilutable groups.

Also included within the scope of this invention is an improved processfor coating a substrate, such as a vehicle body or part thereof, usingthe coating composition disclosed herein.

“Water-reducible” or “water-dilutable” as used herein means the materialis soluble in water or is dispersible in water after neutralization.

DETAILED DESCRIPTION OF THE INVENTION

The anti-crater agent is readily incorporated into the electrocoatingcomposition since it is compatible with the other constituents of thecomposition. The anti-crater agent remains stable in the composition andin the electrocoating bath for extended periods of time underconventional bath operating conditions since it is not reactive with theother constituents in the composition. The anti-crater agentsignificantly reduces and often eliminates craters in electrodepositedcoatings and forms smooth and even finishes and the additive does notadversely affect adhesion of subsequent coating layers applied thereoverand other properties of the electrocoating bath or finishes of theelectrocoating composition.

The anti-crater additive is used in an electrocoating composition in asufficient amount to significantly reduce or eliminate cratering in theelectrodeposited finish. Generally, the anticrater agent is used in theelectrocoating composition at a level of at least 0.5% by weight, basedon the total weight of binder solids in the electrocoating compositionand preferably, it is used at a level of about 0.5-10% by weight. Morepreferably, about 1-5% by weight of the anti-crater agent is used. Thebinder of the electrocoating composition is a blend of an epoxy amineadduct and a blocked polyisocyanate crosslinking agent.

The anti-crater agent is prepared by first reacting a hydroxy functionalcyclic carbonate with a carboxylic acid anhydride in a conventionalmanner under conditions sufficient to ring open the anhydride and formadduct with a primary carboxyl group at one terminus and a cycliccarbonate at the other terminus. This reaction is generally conducted attemperature of about 90 to 150 degree C. in the presence of catalystuntil the reaction is substantially complete. Examples of the catalystsare triphenylphosphine or ethyltriphenylphosphonium iodide. Preferablyfor the desired ring opening reaction and formation of an adduct havingone primary carboxyl group, a carboxylic acid anhydride is used.Reaction of the hydroxy functional cyclic carbonate with a carboxylicacid instead of an anhydride would require esterification bycondensation eliminating water, which would have to be removed bydistillation. Under these conditions, this would promote undesiredpolyesterification, which should be avoided.

The time of reaction can vary somewhat depending principally upon thetemperature of reaction. Usually the reaction time will be from as lowas 10 minutes to as high as 24 hours.

The equivalent ratio of anhydride to hydroxy on the cyclic carbonate ispreferably at least about 0.8:1 to about 1.2:1 (the anhydride beingconsidered monofunctional) to obtain maximum conversion to the desiredreaction product, with the ratio of 1:1 being preferred. Ratios lessthan 0.8:1 can be used but such ratios result in increased formation ofless desired polyesterification products.

Among the cyclic carbonates that can be used are those, which containactive hydrogen atoms with one or more hydroxy functional groups. Thesecyclic carbonates are well known in the art. Examples include hydroxyfunctional cyclic carbonates of various ring sizes as are known in theart, although five-membered-ring or six-membered-ring cyclic carbonatesare generally preferred. Five-membered rings are more preferred, due totheir greater degree of commercial availability. Typically usefulfive-membered cyclic carbonates that contain a hydroxyl group are1,3-dioxolan-2-one-4-propanol, 1,3-dioxolan-2-one-butanol,1,3-dioxolan-2-one-pentanol and the like. Typically useful 6-memberedcyclic carbonates that contain a hydroxyl group are1,3-dixolan-2-one-2,2-diethylpropanol,1,3-dioxolan-2-one-2,2-dimethylpropanol and the like. A five-memberedcyclic carbonate carrying a 1,3-dioxolan-2-one group, such as1,3-dioxolan-2-one-propanol or commonly called glycerin carbonate isparticularly preferred.

Among the anhydrides which can be used in the formation of the ester orcarboxyl groups are those, which exclusive of the carbon atoms in theanhydride moiety contain from about 2 to 30 carbon atoms. Examplesinclude aliphatic, including cycloaliphatic, olefinic and cycloolefinicanhydrides and aromatic anhydrides. Substituted aliphatic and aromaticanhydrides are also included within the definition of aliphatic andaromatic provided the substituents do not adversely affect thereactivity of the anhydride or the properties of the resultantpolyester. Examples of substituents would be halogen, alkyl and alkoxygroups. Aromatic anhydrides are generally not preferred due to theirpoor weathering characteristics.

Typically useful aliphatic acid anhydrides are phthalic anhydride,maleic anhydride, succinic anhydride, hexahydrophthalic anhydride,tetrahydrophthalic anhydride, and methylhexahydrophthalic anhydride.Examples of other useful aliphatic acid anhydrides includehexadecenylsuccinic anhydride, octenylsuccinic anhydride,octadecenylsuccinic anhydride, tetradecenylsuccinic anhydride,dodecenylsuccinic anhydride, and octadecenylsuccinic anhydride. Thelatter class of anhydrides are generally preferred since they containlong chain hydrocarbons of at least 4 carbon atoms, preferably of atleast 6 to 18 carbon atoms, exclusive of the carbon atoms in theanhydride moiety, which provide for good stability and the properhydrophilic/hydrophobic balance in the final coating composition. Acidanhydrides such as dodecenylsuccunic anhydride and octadecenylsuccinicanhydride are particularly preferred.

Subsequently, the carboxyl groups formed by ring opening the anhydridering are optionally, but preferably, chain extended with amonofunctional epoxy resin, particularly a monoglycidyl ether, toconvert the carboxyl groups to hydroxyl groups and then with additionalacid anhydride to convert the hydroxyl groups back to acid groups. Theadduct is preferably chain extended in this manner in order to introduceadditional hydrocarbon chains into the molecule for better stability andbetter hydrophilic/hydrophobic balance.

The monoepoxy compound is as noted above, added after the desiredcompletion of the first reaction. The monoepoxy-acid anhydride chainextension reaction is generally conducted under the same conditions asin the first reaction.

Among the monoglycidyl ethers which can be used in the chain extensionreaction are those that have 1,2-epoxy equivalency of about 1, that is,monoepoxides which have on an average basis one epoxy group permolecule. These epoxy compounds can be saturated, unsaturated,aliphatic, cycloaliphatic, aromatic or heterocyclic. They may containsubstituents such as halogen, hydroxy, ether, alkyl and/or aryl groupsprovided the substituents do not adversely affect the reactivity of theadduct or the properties of the resultant polyester.

The preferred monoepoxy compounds are those, which exclusive of thecarbon atoms in the epoxy moiety contain from about 4 to 18 carbonatoms. Particularly preferred are monoglycidyl ethers of long chain,i.e., C₄ or higher, monohydric alcohols. Representative examples ofmonoglycidyl ethers that may be used to advantage include alkyl,cycloalkyl, alkylalkoxysilane, aryl and mixed aryl-alkyl-monoglycidylethers, such as, o-cresyl glycidyl ether, phenyl glycidyl ether, butylglycidyl ether, octyl glycidyl ether, dodecyl glycidyl ether,glycidoxypropyltrimethoxysilane, glycidoxypropyltriethoxysilane,2-ethylhexyl glycidyl ether. 2-Ethylhexyl glycidyl ether or thecombination of glycidoxypropyltrimethoxysilane and 2-ethylhexyl glycidylether is particularly preferred. Other useful long chain epoxy compoundshaving one epoxy group will readily occur to one skilled in the art.

Among the acid anhydrides, any of the aforementioned acid anhydrides canbe used in the chain extension reaction.

The equivalent ratio of carboxyl to hydroxyl groups in this chainextension reaction is preferably at least about 0.8:1 to about 1.2:1 toobtain maximum conversion to the chain extended adduct, with the ratioof 1:1 being particularly preferred. The reaction wherein the acidgroups are converted to hydroxyl groups is carried out until an acidvalue of less than 20 mg KOH/g is reached; preferably less than 5 mgKOH/g. The subsequent reaction wherein the hydroxyl groups are convertedto carboxyl groups is carried out until an acid value is greater than 40mg KOH/g is reached; preferably greater than 60 mg KOH/g.

In the next step of the synthesis, the carboxyl groups formed on thechain extended or, if desired, non-chain extended adduct aresubsequently reacted with a chemical bridging or coupling agent havingtwo or more sites reactive with carboxyl groups to form a di- or higheradduct (i.e., branched polyester adduct) with terminal cyclic carbonategroups.

The coupling agent is as noted above, added late in the resin reactionsequence when essentially all of the previous reactants have reacted.

The level of chemical coupling agent is primarily selected, relative tothe carboxyl groups, to secure an acid number in the range of 0 to 10,for each 100 grams of resin, to provide the best balance of watersolubilization and low excess carboxyl value.

The reaction with coupling agent is carried under the same conditions asused above and proceeds until the desired acid level is obtained.

The chemical coupling agents used to form the anti-crater agent includepolyfunctional epoxy resins that have a 1,2-epoxy equivalency of abouttwo or more, that is, polyepoxides which have on an average basis two ormore epoxy groups per molecule. These epoxy compounds can be saturated,unsaturated, cyclic, acyclic, aliphatic, cycloaliphatic, aromatic orheterocyclic. They may contain substituents such as halogen, hydroxy,ether, alkyl and/or aryl groups provided the substituents do notadversely affect the reactivity of the adduct or the properties of theresultant polyester.

The preferred polyepoxides are polyglycidyl ethers of cyclic polyols.Particularly preferred are polyglycidyl ethers of polyhydric phenolssuch as bisphenol A. These polyepoxides can be produced byetherification of polyhydric phenols with epihalohydrin or dihalohydrinsuch as epichlorohydrin or dichlorohydrin in the presence of alkali.Examples of polyhydric phenols are 2,bis-(4-hydroxyphenyl)ethane,2-methyl-1,1-bis-(4-hydroxyphenyl)ethane,2-methyl-1,1-bis-(4-hydroxyphenyl)propane,2,2-bis(4-hydroxy-3-tertiarybut ylphenyl)propane,1,1-bis-(4-hydroxyphenol)ethane, bis-(2-hydroxynaphthyl)methane,1,5-dihydroxy-3-naphthalene or the like.

Besides polyhydric phenols, other cyclic polyols can be used inpreparing the polyglycidyl ethers of cyclic polyol derivatives. Examplesof other cyclic polyols would be alicyclic polyols, particularlycycloaliphatic polyols, such as 1,2-bis(hydroxymethyl)cyclohexane, 1,3bis-(hydroxymethyl)cyclohexane, 1,2 cyclohexane diol, 1.4, cyclohexanediol and hydrogenated bisphenol A.

The polyepoxides have molecular weights of at least 200 and preferablywithin the range of 200 to 3000, and more preferably about 340 to 2000.

The polyepoxides can be chain extended with a polyether or a polyesterpolyol, which enhances flow and coalescence. Typical useful chainextenders are polyols such as polycaprolactone diols such as Tone 200®series available from Union Carbide Corporation and ethyoxylatedBisphenol A such as SYNFAC 8009® available from Milliken ChemicalCompany.

Examples of polyether polyols and conditions for chain extension aredisclosed in U.S. Pat. No. 4,468,307. Examples of polyester polyols forchain extension are disclosed in Marchetti et al U.S. Pat. No. 4,148,772issued Apr. 10, 1979.

The terminal cyclic carbonate groups on the di- or higher branchedpolyester adduct are then reacted in a subsequent reaction with apolyamine compound that contains at least one free tertiary amine groupand also additionally contains a primary amine or secondary amine group,to form the final branched polyester-amine adduct that contains terminaltertiary amine groups. Typical polyamines containing at least onetertiary amine and one primary amine or secondary amine that are usedinclude N,N-dimethylaminopropylamine, aminopropylmonomethylethanolamine,N,N-diethylaminopropylamine, aminoethylethanolamine,N-aminoethylpiperazine, aminopropylmorpholine,tetramethyldipropylenetriamine and diketimine (a reaction product of 1mole diethylenetriamine and 2 moles methyl isobutyl ketone).N,N-dimethylaminopropylamine is particularly preferred. Typically afterthe adduct with cyclic carbonate terminal groups described above isformed, the amine that contains primary or secondary amine functions inaddition to the tertiary amine functions, and additional solvent areadded to the reaction solution and the reaction is continued at elevatedtemperature until all the cyclic carbonate groups are reacted andconverted to terminal tertiary amine groups. The amount of polyaminerequired will vary from case to case depending upon the desired degreeof water solubility needed for the particular end use application.Generally, an equimolar amount of amine to cyclic carbonate is used,however a slight excess of carbonate is acceptable.

To further enhance crater resistance property, a portion of thepolyamine used in the above reaction can be replaced with an aminofunctional alkylalkoxysilane compound, which is also reactive with theterminal cyclic carbonate groups and capable of converting these groupsto terminal alkoxy silane groups. Typical useful aminoalkylalkoxysilanecompounds are gamma-aminopropyltriethoxysilane,gamma-aminopropyltrimethoxysilane, andN-(2-aminoethyl)-3-aminopropyltrimethoxysilane.Gamma-aminopropyltrimethoxysilane is particularly preferred. In apreferred embodiment, blends of polyamines and aminoalkylalkoxysilanesare used. Preferably, in these blends about 5 to 40 mole % of thepolyamine is substituted with an aminoalkylalkoxysilane, with about 5 to20 mole % substitution being especially preferred.

The resultant anti-crater additives that are produced above are of lowto intermediate molecular weight, having a number average molecularweight of aboutl,000-10,000, preferably −2000-6000, as determined by GPC(Gel Permeation Chromatography) using polystyrene as the standard.

The additive is emulsified in water with an organic or inorganic acid(mentioned below) to fully or partially neutralize the tertiary aminefunctionality. The anti-crater additive can then be added to theelectrocoating composition at almost any time. It can be added to theprincipal emulsion, to the bath or to the pigment paste. In the pigmentpaste, pigment is ground with a resin, which can be the anticrateragent, which also functions as a pigment dispersing resin.

Most principal emulsions used in an electrocoating composition comprisean aqueous emulsion of a binder of an epoxy amine adduct blended with acrosslinking agent which has been neutralized with an acid to form awater soluble product.

The anti-crater agent is potentially usable with a variety of differentcathodic electrocoat resins, but the preferred resin is the typicalepoxy-amine adduct of the prior art. These resins are generallydisclosed in U.S. Pat. No. 4,419,467, which is incorporated byreference.

Typical acids used to neutralize the epoxy-amine adduct as well as theadditive to form water dispersible cationic groups are lactic acid,acetic acid, formic acid, sulfamic acid and the like.

Preferred crosslinkers for the above resins are also well known in theprior art. These are aliphatic, cycloaliphatic and aromatic isocyanatessuch as hexamethylene diisocyanate, cyclohexamethylene diisocyanate,toluene diisocyanate, methylene diphenyl diisocyanate and the like.These isocyanates are pre-reacted with a blocking agent such as oximes,alcohols, or caprolactams which block the isocyanate functionality,i.e., the crosslinking functionality. Upon heating the blocking agentsseparate, thereby providing a reactive isocyanate group and crosslinkingoccurs. Isocyanate crosslinkers and blocking agents are well known inthe prior art and also are disclosed in the aforementioned U.S. Pat. No.4,419,467.

The cathodic binder of the epoxy amine adduct and the blocked isocyanateare the principal resinous ingredients in the electrocoating compositionand are usually present in amounts of about 30 to 50% by weight ofsolids of the composition. To form an electrocoating bath, the solidsare generally reduced with an aqueous medium.

Besides the binder resin described above, the electrocoating compositionusually contains pigment, which is incorporated into the composition inthe form of a pigment paste. The pigment paste is prepared by grindingor dispersing a pigment into a grinding vehicle and optional ingredientssuch as wetting agents, surfactants, and defoamers. Any of the pigmentgrinding vehicles that are well known in the art can be used or theanticrater agent of this invention can be used. After grinding, theparticle size of the pigment should be as small as practical, generally,the particle size is about 6-8 using a Hegman grinding gauge.

Pigments which can be used in this invention include titanium dioxide;carbon black, iron oxide, clay and the like. Pigments with high surfaceareas and oil absorbencies should be used judiciously because these canhave an undesirable affect on coalescence and flow of theelectrodeposited coating.

The pigment to binder weight ratio is also important and should bepreferably less than 0.5:1, more preferably less than 0.4:1, and usuallyabout 0.2 to 0.4:1. Higher pigment to binder weight ratios have beenfound to adversely affect coalescence and flow.

The coating compositions of the invention can contain optionalingredients such as wetting agents, surfactants, defoamers and the like.Examples of surfactants and wetting agents include alkyl imidazolinessuch as those available from Ciba-Geigy Industrial Chemicals as “AmineC”, acetylenic alcohols available from Air Products and Chemicals as“Surfynol 104”. These optional ingredients, when present, constitutefrom about 0.1 to 20 percent by weight of binder solids of thecomposition.

Optionally, plasticizers can be used to promote flow. Examples of usefulplasticizers are high boiling water immiscible materials such asethylene or propylene oxide adducts of nonyl phenols or bisphenol A.Plasticizers are usually used at levels of about 0.1 to 15 percent byweight resin solids.

The electrocoating composition of this invention is an aqueousdispersion. The term “dispersion” as used within the context of thisinvention is believed to be a two-phase translucent or opaque aqueousresinous binder system in which the binder is in the dispersed phase andwater the continuous phase. The average particle size diameter of thebinder phase is about 0.1 to 10 microns, preferably, less than 5microns. The concentrations of the binder in the aqueous medium ingeneral is not critical, but ordinarily the major portion of the aqueousdispersion is water. The aqueous dispersion usually contains from about3 to 50 percent preferably 5 to 40 percent by weight binder solids.Aqueous binder concentrates which are to be further diluted with waterwhen added to an electrocoating bath, generally have a range of bindersolids of 10 to 30 percent weight.

The following example illustrates the invention. All parts andpercentages are on a weight basis unless otherwise indicated.

EXAMPLE

Preparation of Anti-Crater Additive I

A highly branched water-reducible polyester was prepared by charging 266parts dodecenylsuccinic anhydride, 125 parts glycerin carbonate and 3parts triphenylphosphine into a suitable reaction vessel and heated to116° C. under a dry nitrogen blanket. The reaction was held at 132° C.until an acid number of 132 to 136 was achieved. 266 parts 2-ethylhexylglycidyl ether and 3 parts triphenylphosphine were then added and thereaction mixture was held at 132 C until an acid number of 0 to 3 wasachieved. 266 parts Dodecenylsuccinic anhydride and 1 parttriphenylphosphine were added and the reaction mixture was held at 132°C. until an acid number of 56 to 62 was achieved. Then 89 partsmethoxypropanol was added and the reaction temperature was dropped to116° C. 187 parts Epon® 828 (diglycidyl ether of bisphenol A) was slowlycharged into the reaction vessel. The reaction mixture was held at 116°C. until an acid number of less than 10 was obtained. 102 partsN,N-dimethylaminopropylamine was added and held at 116° C. for one hour.The reaction mixture was then dispersed in an aqueous medium of 2510parts of deionized water and 157 parts lactic acid (46% concentration)and mixed for 30 minutes. The resulting adduct solution had anonvolatile content of 30% in water.

Preparation of Anti-Crater Additive II

A highly branched water-reducible polyester was prepared by charging 266parts dodecenylsuccinic anhydride, 125 parts glycerin carbonate and 3parts triphenylphosphine into a suitable reaction vessel and heated to116° C. under a dry nitrogen blanket. The reaction was held at 132° C.until an acid number of 132 to 136 was achieved. 266 parts 2-ethylhexylmonoglycidyl ether, 47 parts gamma-glycidoxypropyltrimethoxysilane and 3parts triphenylphosphine were then added and the reaction mixture washeld at 132° C. until an acid number of 0 to 3 was achieved. 266 partsDodecenylsuccinic anhydride and 1 part triphenylphosphine were added andthe reaction mixture was held at 132° C. until an acid number of 56 to62 was achieved. Then 89 parts methoxypropanol was added and thereaction temperature was dropped to 116° C. 187 parts Epon® 828(diglycidyl ether of bisphenol A) was slowly charged into the reactionvessel. The reaction mixture was held at 116° C. until an acid number ofless than 10 was obtained. 87 parts N,N-dimethylaminopropylamine and 33parts gamma-aminopropyltrimethoxysilane were added and held at 116° C.for one hour. The reaction mixture was then dispersed in an aqueousmedium of 2531 parts deionized water and 133 parts lactic acid (46%concentration) and mixed for 30 minutes. The resulting adduct solutionhad a nonvolatile content of 30% in water.

Preparation of Crosslinking Resin Solution

An alcohol blocked polyisocyanate crosslinking resin solution wasprepared by charging 317.14 parts of Mondur® MR (methylene diphenyldiisocyanate), 105.71 parts of methyl isobutyl ketone and 0.06 parts ofdibutyl tin dilaurate into a suitable reaction vessel and heated to 37°C. under a nitrogen blanket. A mixture of 189.20 parts of propyleneglycol mono methyl ether and 13.24 parts of trimethylolpropane wasslowly charged into the reaction vessel while maintaining the reactionmixture below 93° C. The reaction mixture was then held at 110° C. untilessentially all of the isocyanate was reacted as indicated by infraredscan of the reaction mixture. 3.17 Parts of butanol and 64.33 parts ofmethyl isobutyl ketone were then added. The resulting resin solution hada nonvolatile content of 30% in deionized water.

Preparation of Chain Extended Polyepoxide Emulsion

The following ingredients were charged into a suitable reaction vessel:520 parts of Epon 828® (Epoxy resin of diglycidyl ether of bisphenol Ahaving an epoxy equivalent weight of 188); 151 parts bisphenol A; 190parts ethoxylated bisphenol A having a hydroxy equivalent weight of 247(Synfac® 8009), 44 parts xylene and 1 part dimethyl benzyl amine. Theresulting reaction mixture was heated to 160° C. under nitrogen blanketand held at room temperature for 1 hour. 2 parts dimethyl benzyl aminewere added and the mixture was held at 147° C. until an epoxy equivalentweight of 1050 was obtained. When the reaction mixture cooled to 149°C., then 797 parts of crosslinker resin solution (from above) was added.When the reaction temperature cooled to 107° C., 58 parts of diketimine(reaction product of diethylenetriamine and methyl isobutyl ketonehaving a nonvolatile content of 73%) and 48 parts of methyl ethanolamine were added. The temperature of the resulting mixture rose and washeld at 120° C. for 1 hour and then dispersed in an aqueous medium of1335 parts deionized water and 61 parts lactic acid (88% lactic acid indeionized water). An additional 825 parts of deionized water was added.The emulsion was kept agitated until the methyl isobutyl ketone wasevaporated. The resulting resin emulsion had a nonvolatile content of38%.

Preparation of Quaternizing Agent

The quaternizing agent was prepared by adding 87 partsdimethylethanolamine to 320 parts 2-ethylhexanol half-capped toluenediisocyanate in the reaction vessel at room temperature. An exothermicreaction occurred and the reaction mixture was stirred for one hour at80° C. 118 parts aqueous lactic acid solution (75% nonvolatile content)was then added followed by the addition of 39 parts 2-butoxyethanol. Thereaction mixture was held for about one hour at 65° C. with constantstirring to form the quaternizing agent.

Preparation of Pigment Grinding Vehicle

The pigment grinding vehicle was prepared by charging 710 parts Epon®828 (diglycidyl ether of bisphenol A having an epoxide equivalent weightof 188) and 290 parts bisphenol A into a suitable vessel under nitrogenblanket and heated to 150° C.-160° C. to initiate an exothermicreaction. The exothermic reaction was continued for about one hour at150° C.-160° C. The reaction mixture was then cooled to 120° C. and 496part of 2-ethylhexanol half capped toluene diisocyanate was added. Thetemperature of the reaction mixture was held at 110° C.-120° C. for onehour, followed by the addition of 1095 parts of 2-butoxyethanol, thereaction mixture was then cooled to 85° C.-90° C. and then 71 parts ofdeionized water was added followed by the addition of 496 partsquarternizing agent (prepared above). The temperature of the reactionmixture was held at 85° C.-90° C. until an acid value of about 1 wasobtained. Preparation of Pigment Paste Ingredient Parts by WeightPigment grinding vehicle (prepared above) 597.29 Deionized Water 1140.97Titanium dioxide pigment 419.28 Aluminum silicate pigment 246.81 Carbonblack pigment 15.27 Barium sulfate pigment 416.38 Dibutyl tin oxide164.00

The above ingredients were mixed in a suitable container until ahomogenous mixture was formed. They were then dispersed by charging themixture into a Eiger mill and then grinding until a Hegman reading of 7or greater was obtained. Preparation of Electrocoating Baths Parts byWeight Ingredient Bath I Bath II Bath III Emulsion 1550.00 1605.001605.00 Deionized Water 1999.00 1998.00 1998.00 Pigment Paste 356.00356.00 356.00 Anticrater Agent 95.00* 42.00** 42.00*** Total 4000.004000.00 4000.00*The anticrater agent used in Bath I comprised a conventional anticrateragent which is the reaction product of Jeffamine ® D2000(polyoxyalkylene diamine) and Epon ®1001 epoxy resin.**The anticrater agent used in Bath II comprised the new anticrateradditive I prepared above.***The anticrater agent used in Bath III comprised the new anticrateradditive II prepared above.

Each of the cationic electrocoating baths were prepared by mixing theingredients together, and then ultrafiltering the mixtures. Each bathwas electrocoated at 240 to 280 volts to obtain 0.8-1.0 mils (20.23-25.4microns). The baths were then compared for crater resistance and PVCsealer adhesion. Bath I served as the control.

ASPP blow out crater test is used to test each bath. Crater resistancewas rated according to the following rating scale of A-E:

-   -   A—0-10% defects    -   B—11-20% defects    -   C—21-40% defects    -   D—41-80% defects    -   E—Greater than 80% defects

The crater resistant rating for Bath I (control) was D. Baths II rated Cand bath III rated B on crater resistance.

Crater resistance of each bath was also measured by an oil contaminationtest. In order to measure carter resistance under the oil contaminationtest, 20 ppm of Quicker oil was added to each bath and mixed for 24hours under low agitation. Each bath was then electrocoated to obtain0.8-1.0 mils film build. For oil contamination test, crater resistancewas rated according to the following rating scale of 1 to 5:

-   -   1—less than 10 craters    -   2—10 to 20 craters    -   3—30 to 50 craters    -   4—50 to 100 craters    -   5—greater than 100 craters

The oil contamination test rating for Bath I was 4, Bath II was 2 andBath III was 1.

To conduct a PVC sealer adhesion test, electrocoated panels were firstprepared by electrocoating cold-rolled steel substrates withelectrocoating baths prepared above at 240V to 280V coating voltage forobtaining 0.8-0.9 mils film thickness. The uncured E-coat panels werethen baked in electric-oven at 182° C. for 10 minutes metal temperature.A commercially available PVC sealer (supplied by Eftec company under thetrade name Togotec® PB209V1) was applied on an electric-oven bakedelectrocoated panel. The thickness of the PVC sealer was 1 mm and bakedat 140° C. for 10 minutes metal temperature. The adhesion was rated passif no sealer can be pulled from electrocoated substrate and fail if nosealer can adhere to e-coated substrate.

The PVC sealer adhesion rating for Bath I was fail, Bath II was pass andBath III was pass.

Various other modifications, alterations, additions or substitutions ofthe compositions and methods of this invention will be apparent to thoseskilled in the art without departing from the spirit and scope of thisinvention. This invention is not limited by the illustrative embodimentsset forth herein, but rather is defined by the following claims.

1. An improved cathodic electrocoating composition, comprising anaqueous carrier having dispersed therein a film forming bindercomprising an epoxy-amine adduct and a blocked polyisocyanatecrosslinking agent; wherein the improvement is the incorporation of ananti-crater agent comprising a highly branched water-reducible polyesterwhich is the reaction product of: (a) a hydroxy cyclic carbonate; (b) analiphatic polycarboxylic acid anhydride; (c) optionally, amonofunctional epoxy resin; (d) a bridging agent selected from the groupconsisting of diepoxy and higher polyepoxy resin; (e) a polyaminecompound selected from the group consisting of (i) a polyamine having atleast one free tertiary amine and one primary or secondary amine group;and (ii) a combination of a polyamine having at least one free tertiaryamine and one primary or secondary amine group, and anaminoalkylalkoxysilane, which reaction product is neutralized in thepresence of acid and water to convert the tertiary amine groups towater-dilutible groups.
 2. The composition of claim 1, wherein thealiphatic polycarboxylic acid anhydride contains a C₄ to C₁₈ linear,branched or cycloaliphatic side chain.
 3. The composition of claim 1,wherein components (a)-(e) are reacted in any workable order.
 4. Thecomposition of claim 1, wherein components (a)-(e) are reacted in theorder given.
 5. A method for the preparation of the anti-crater agent asclaimed in claim 1, wherein the hydroxy cyclic carbonate compound (a) isfirst reacted with acid anhydride compound (b) to form an adductcontaining an acid group, wherein the acid group is reacted with thebridging agent (d) to form a di- or higher adduct respectively withterminal cyclic carbonate groups; wherein the terminal cyclic carbonategroups are subsequently reacted with a polyamine compound (e) resultingin an adduct with terminal amine groups which are then neutralized withacid resulting in a water-reducible polyester.
 6. The method of claim 5,wherein prior to reacting the adduct containing an acid group formed inthe first reaction with a bridging agent, the adduct is further reactedwith a monofunctional epoxy resin (c) to convert the acid group to ahydroxyl group with resulting acid value less than 20 mg KOH/g and forma chain extended adduct containing a hydroxyl group, and wherein theadduct containing the hydroxyl group is subsequently reacted withadditional acid anhydride (b) to form a further chain-extended adductcontaining an acid group with resulting acid value greater than 40 mgKOH/g, which is then reacted with the bridging agent.
 7. A method ofpreparing a cathodic electrocoating composition comprising the followingsteps in any workable order: (a) preparing an epoxy-amine adduct; (b)preparing a blocked polyisocyanate crosslinking agent; (c) blending theepoxy-amine adduct with the blocked polyisocyanate crosslinking agent;(d) neutralizing the epoxy-amine adduct with an organic acid to form anemulsion; (e) blending the emulsion with a pigment paste; and (f)incorporating an additive agent into the electrocoating composition;wherein the additive consists essentially of the reaction product ofclaim 1.